Reciprocating slat conveyors comprise a plurality of side by side conveyor slats that are driven in one direction for advancing a load and are retracted in the opposite direction. Some reciprocating slat conveyors are divided into both "sets" and "groups" of conveyor slats. The slats of each "set" are moved together. Each "group" includes one slat from each "set." In some slat conveyors, all of the slats are driven in unison, in the conveying direction, and are then retracted sequentially, one set at a time. It has also been proposed to drive a majority of the conveyor slat sets in the conveying direction while retracting the remaining conveyor slat sets, to continuously move the load on the conveyor. An example of the first type of conveyor is disclosed in my U.S. Pat. No. Re. 35,022, granted Aug. 22, 1995. An example of the second type of conveyor is disclosed in my U.S. Pat. No. 4,580,678, granted Apr. 8, 1986.
Conveyor slats have been constructed from aluminum, steel and structural plastic. The aluminum and structural plastic slats are formed by extrusion. The steel slats are roll formed. Example aluminum slats are disclosed by my U.S. Pat. No. 4,785,929, granted Nov. 22, 1988. Example steel slats are disclosed by my U.S. Pat. No. Re. 33,196, granted Apr. 10, 1990. Example structural plastic slats are disclosed by my U.S. Pat. No. 5,447,222, granted Sep. 5, 1995, and by U.S. Pat. No. 5,301,798, granted Apr. 12, 1994, to Arthur L. Wilkins. The Wilkins U.S. Pat. No. 5,301,798 discloses forming slats by extrusion. My U.S. Pat. No. 5,447,222 discloses forming slats by co-extrusion.
The term pultrusion is used to describe both a process of manufacture and the products manufactured by the process. The process begins with the delivery of an organized schedule of reinforcement fibers from storage creels through guides into an impregnation zone where the reinforcement fibers are saturated with a liquid thermal setting resin that is reactive at elevated temperatures yet stable at ambient temperatures. After saturation, the reinforcement fibers are moved from the impregnation zone to and through formers in which they are formed progressively in stages to remove excess resin and to achieve the approximate geometry of the finished profile. Following this pre-forming step, the materials are compacted into the final densified structure as they enter the tapered mouth of a pultrusion die. The pultrusion die is a self contained reaction vessel in which rapid polymerization of the resin occurs when exposed to the elevated die temperature environment. The moving material is constrained within the close tolerances of the die as it is being cured. Upon achieving a sufficient level of polymerization, the material is pulled out from the die and is generally allowed an interval of movement through space so as to cool by natural or forced convection to a level below which the pulling device, employed to grip and pull the product, will not damage the composite profile. The pulling mechanism is followed by a flying cut-off saw which enables the product to be cut to length without interruption of the continuous pull motion.
There is a need for conveyor slats that are chemical resistant and non-corrosive and yet are light weight, tough and strong. There is also a need for conveyor slats formed by pultrusion that have desirable surface characteristics, and in particular to a way of forming the conveyor slats to include a surface veil made from a thermoplastic material. A principal object of the present invention is to provide such a conveyor slat or other members.